Ammonium phosphates have many utilities in industry including such technical uses as fertilizers fire proofing textiles, paper, wood, and vegetable fibers, impregnating lamp wicks, flux for soldering tin, copper, brass and zinc, hard surface cleaners, corrosion inhibitors and in forest fire retardants. They are also useful in food and dentifrice applications such as in purifying sugar, in yeast cultures, oral compositions and baking powder.
Monoammonium phosphate and diammonium phosphate (hereinafter referred to as ammonium phosphates) prepared from pure acids (P.sub.2 O.sub.5 /water derived from phosphorus burners) rather than from the wet acid process are particularly known for their tendency to cake severely and much effort is used to break up the cake upon delivery of the product. As can be seen from the above noted industrial uses, large amounts of monoammonium and diammonium phosphates are used and therefore shipping containers of large scale size are employed in the transport of these material. Caking is a particular disadvantage when there is presented the occasion of large amounts of these phosphates to cake into shapes of considerable size requiring so much effort as to affect the economics of their use.
Agents employed to inhibit caking of materials in the past have relied upon the property of hygroscopisity or the use of hygroscopic agents to at least minimize caking. Such materials included corn sugar or glycerine, sorbital and propylene glycol. These materials are noted in U.S. Pat. No. 2,770,548 to Hall et al. It is also noted in said patent that small or trace amounts of metal ions function as oxidation catalysts in nitrite converting it to the nitrate. The use of polyphosphate, such as sodium polyphosphate, was added to sequester the metal ions. However, as indicated in the above noted patent, the sequestration of the metal ions did not reduce the tendency of the nitrites to cake. The above noted Hall patent teaches that the hygroscopic caking inhibitor for meat-curing compositions is improved with the addition of an alkaline alkali metal orthophosphate such as trisodium or disodium phosphate or the potassium analogs. Such orthophosphates were employed in the range of from 2% to 5% by weight. However the meat treating compositions disclosed by this patent did not contain any ammonium phosphates.
Various phosphate salts are well know for their utility in detergents. A composition containing monoammonium or diammonium phosphate as a cleaning agent is disclosed in U.S. Pat. No. 3,354,092 to Perry wherein orthophosphates and tripolyphosphates were included for their detergency effect. No caking inhibition was attributed to these salts and they were employed in amounts to provide active cleaning effect ranging from 40% to 97% of the composition while the ammonium phosphates represented only about 0% to about 34% of the composition.
More recently there has been disclosed a water soluble potassium phosphate caking inhibitor for fertilizer compositions in U.S. Pat. No. 5,286,272 to Biamonte et al. More particularly, tripotassium phosphate, which is highly water soluble and hygroscopic, was employed in as little as 0.25% up to 5%, by weight, in fertilizer compositions containing amounts of monoammonium and diammonium phosphates in the range of from 16% to 32% along with major amounts of nitrates such as ammonium and potassium nitrates or urea. It has been found that caking tendency increases as the ammonium moeity of the phosphate increases. In large industrial production of ammonium phosphates it is important that the same caking inhibitor can be employed for either monoammonium phosphate or the more severely affected diammonium phosphate. Water solubility is important for most uses of the ammonium phosphates and the use of insoluble caking inhibitors leave undesirable precipitates. Previously water soluble caking inhibitor of adequate activity to be employed in small amounts were unknown for use in monoammonium and diammonium phosphate compositions. There is a need for highly active water soluble caking inhibitors for use in large quantities of monoammonium and diammonium phosphates thereby improving the economics in the use of these materials.